1. Field of the Invention
The present invention relates to a suction-purging unit and a suction-purging method for use in an ink jet printer.
2. Description of the Related Art
The quiet operation and compact size of ink jet printers has propelled them into popular use in offices for printing desired characters and graphics onto print media upon ink ejection.
However there has been known a problem with conventional ink jet printers in that contaminants such as dirt and paper particles clinging to the head surface, or bubbles generated in the ink pathway, cause inaccurate discharge of ink from the nozzles in the head. Nozzles also can become clogged by ink that has solidified therein, ink films that have adhered to the walls thereof, or contamination within the ink.
Three general measures which have been applied to relieve the above problems are listed below.
1. Pressure purging wherein air bubbles within the nozzle and contamination adhering to the nozzle tips are discharged along with ink by pressurizing or compressing air applied to a rear portion of an ink tank. PA1 2. Suction-purging (such as described in Japanese Patent Application Kokai No. Sho-58-177370) in which a capping suction unit device is mounted to the head so as to cover all the nozzles formed therein, whereupon air bubbles within the nozzle and contamination adhering to the nozzle tips are sucked therefrom by decompression. PA1 3. Pressure/suction-purging wherein a combination of the first two methods is applied.
Although advantageous because of their relatively simple structure, pressure purging units have a known problem in that they discharge ink from all nozzles during purging operations, thereby wasting a great deal of ink. Also, unless all nozzles are uniformly wet at their interiors, effectiveness of purging will be disparate between nozzles.
There has been known a problem with capping suction-purging units in that the larger the head, or the more nozzles are formed therein, the more difficult producing a proper seal between the capping suction device and the head becomes. To produce a proper seal requires increasing the complexity of the capping suction device, the power of the pump, or both.
An additional problem occurs in ink jet printers which use hot-melt ink in that the hot-melt ink hardens during suction-purging. Conventional suction-purging units are not appropriate for use with hot-melt ink, that is, if the power of the suction pump is too low, suction is insufficient, and if too high, ink is sucked within the pump which later causes insufficient suction when the ink hardens.
Also certain components of hot-melt ink evaporate after the hot-melt ink is heated for long periods at a temperature above its melting point. When the hot-melt ink cools, these evaporated components crystallize to the walls of the ink chamber as ink snow. In conventional suction-purging devices, these evaporated components are sucked into the pump where they later harden and lower the suction power of the pump.